Of the studies that control for home environment, all indicate strong environmental effects. One of these studies is consistent with moderate African genetic superiority and one is consistent with substantial European genetic superiority. Thus, the most relevant studies provide no evidence for genetic superiority for one race or the other while providing strong evidence for a substantial environmental contribution to the B/W IQ gap. Almost equally important, rigorous
interventions effect IQ and cognitive skills at every stage of the life course, and the evidence on convergence clearly shows that the B/W IQ gap has narrowed in recent decades.3
The question "What portion of the 15 point IQ difference between blacks and whites is genetic?" simply makes no sense. To begin with, the empirical gap is currently substantially less than that. Moreover, with the exception of Herrnstein and Murray, few investigators have ever suggested that the entire gap might be genetic in nature. Jensen, one of the best-known proponents of the view of European genetic superiority, estimates that the genetic gap is about seven points [ref.]. As Block (1995) has suggested, the reference point should not be a gap of 15 points or any other specific figure. Rather, it makes more sense to ask how far, and in what direction, the genetically-based difference between the races differs from zero.
If in fact it makes sense to ask the genetic question at all. All evidence points to two extraordinarily important conclusions. First, if there are genetically-determined differences between the races in IQ, they are not sufficiently large to show up with any regularity in studies with a wide range of methodologies. Second, interventions designed to reduce the difference between blacks and whites are effective at every age level. Surely research efforts are best directed at improving these interventions rather than trying to wring blood from a genetic turnip.